Lens-testing instrument.



A. H. EMERSONL LENS TEsTTNG INSTRUMENT.-

APPLICATION FILED MAY 3l. l9l3.

Patented Oct. 2, 1917.

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ALFRED H. EMERSON, OF SOUTHBRIDGE, MASSACHUSETTS,l ASSIGNCB TO .AMERICAN OPTICAL COMPANY, F SOUTHBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

Application filed May-31, 1913. Serial No. 771,021.

To all whom t may concern: v

Be it known that I, ALFRED H. EMERSON, a subject of the King of England, residing at Southbridge, in the county ofWorcester and State of Massachusetts, have invented certain new and useful Improvements in Lens-Testing Instruments, of which the following is a specification.

My invention relates to improvements in `lens testing instrumentsy and has particular jects of my invention is to provide an instru-j A ment making use of this principle of neutra-lization which shall indicate whether the lensesrare correctly neutralized or not.

A further object of my` invention is the provision of an instrument which in addition to indicating the neutralization or lack of neutralization of the. lenses, will also serve to measure the residual power, if any, and thus indicate the variation.

A further object of my invention is the provision of an instrument in which the lens may be tested against rany standard and will serve to measure and denote the variation, if any, betweenl the lens being tested and the said standard, such standard in ordinary use being' either a Vneutralizing set or trial case lens.

A further object of my invention is to provide a means of locating the optical center of the lens or the amount of prism in a lens or the power of any plane prism or compound sphere and cylinder and prism,-

in other words, any lens which isprismatic may be correctly measured by this system;

' or for locating'l the principal meridian of compound lenses. By compound lenses we mean lenses of any formv which have cylinment which will measure lens within' the range of a trial case,

error only being indicated by the scale, irredrical eie'ct as well as spherical.

A further object is to provide an instruthe error in ailily t e Specification of Letters'Patent.

Patented oct. 2, 1917.

spective of the power of the lens being tested.

A further object is to provide a true method of neutralizing so that one can dis-` regard the magniiication or telescopic e'. ct present in thick lenses.

Another object of my `invention is the provision of an instrument as above set forth which shall have a practically unlimited range of use in testing both high and vlow powers of positive and negative lenses andwhich shall be extremely compact in form and convenient for -everyday use. Another object of-l my vinvention is the provision of an instrumentI in which the location of the various parts may be varied as desired to permit of alteration of the form of the4 instrument without altering the relative action of the parts.

@ther objects and advantages of my iinproved instrument should be readily ap arent by reference to the following speci cation, taken in conjunction with the accompanying drawings, forming a part thereof, and it will be understood that I am to make any modifications in the specified details'of construction shown and described within the scope of the pending" claims without departing from or exceeding the spirit of j my invention. u igure 'I represents a diagrammatic view, illustrating the use of my instrument, the parts being arranged other. l

Fig. II represents a similar diagrammatic view, in which the lens being tested does not exactly neutralize with the lens of opposite known power, one form oii the adjustment of theV system necessary to compensate for this lack of neutralization being indicated in dotted lines.

Fig. III represents a plan view, partially in sectionz of a convenient form o my instrument in which means are employed for changing the pathof the light rays in the instrument.

Fig. IV re resents a sectional view on the line IV- V of Fig. III. Y

Fi V represents a similar View on the `line -V of Fig. III.

Fig. VI represents a view `of the image cast on the image screen when the lens being tested is correct in power.

Fig. VII represents a view of the `image in alinement with each p l l when thelens has error in the vertical meridian only.

Fig. VIII is a similar view when the error is equal in all meridians.

Fig. .IX represents a similar viewwhen the error is unequal in the two principal meridians.

-Fig. X is asimilar view when the'axis of a compound lens is incorrect.

Fig. XI represents a similar view, then dotted lines showing the displacement due tovprismatic effect.

Fig.

` of my instrument showing a marking atvters of reference are employed to denote 'cor- I(it) l responding parts throughout" the several views, .the numeral I 'designates'the frame of my instrument which may be of any desired Vform. j

In'A Fig. III I have illustrated the same j as laid out in a rightangle, this form placa ing the lens to be tested and master lens y close to the operator and, fat the saine time, y causing the lmage to lbe directly in front so that it may be readil yiewedwithout the necessity of change o position by the operator. Mounted on the base 1, as illustrated 1n Fig. III, is the casing or sheath 2, in-

closing the projection portion of my instrument which serves to produceor project parallel rays. To accomplishthis result I employ a s uitable source of illumination 3, havingdlsppsed in front thereof the object screen 4', w ich is disposed at the principal focus of the collimating lens 5 at the inner end of the casing 2.

In that form of my invention here illustrated, I have made the object in the. form of an illuminated cross, as shown in Fig. V, but itwill be understood that this form may be varied as desired.- It will be readily understood by those conversant with the fopti- 1 cal art that the casing 2 and. parts inclosed thereby altogether form usual construction of collimator and that l' do not wish to be limited to the siccied details of construction here descri ed but may, with equal facility, employ any other well known means for producing the parallel rays without varying the spirit or operation of my inventiom'the main idea being that of having XII. represents a fragmentary view advance thereof, at the principal focus of said-lens 9, is a screen 10 f or receiving the ima e of the object 4. This screen is preferab y inclosed by a darkened hood 11, in order that the luminous image or images on the screen can be more easily seen in ordi-4 nary daylight.

When my system as above described is in exact and correct adjustment, the image on the screen 10 is clear and sharply defined, while if the system is at all out of focus, the image will appear on the screen but will be more or less blurred according to the amount of error in the system. To enable persons with but slight optical knowledge to readily perceive whether the system is in exact focus or not, I preferably place adjacent the converging lens 9, a suitable diaphra m 12, which I have illustrated as a cross, alt ough it will be understood that other forms may be employed as desired, the arms of the cross being disposed in parallel relation to those 4of the object 1. With thisV diaphragm A1n position, if the instrument is in exact focus an image such as shown in Fi VI w1ll appear on the screen with the lines clear and sharp, but should the same be out offocus, double lines appear.

To use my instrument for testing lenses, I place a convenient holder 13 anywhere between the collimator and the convergm lens in the path of the parallel rays, an place within this holder a neutralizing lens 14 of opposite power or .powers to the lens to be tested. The lens' to be tested is then held in close contact with the neutralizing lens and the image of the cross upon the screen 10 observed. Should 'this remain single, the lens 4is correct. Should any of the lines appear double, it indicates that the ured by several methods. The preferable method for measurement of this error is that of shifting the converging lens 9 either lens has anerror', which error can be measl ated to denote the error in the lens being :,sunou lens is necessary for measurement of small amounts of error in the lens, it is to be understood thatl I do not wish to limit myself to this particular construction since the same result may be attained b adjustment y of either the object screen l, t e collimator lens 5, the screen '10, or by introducing a compensator such as shown in Fig. XIII, into the path of the parallel rays. This compensator comprises a air of lenses of opposite but slightly diifermg powers, separated `an amount necessary to makethem neutral. Increase or decrease of this separation varies the power in the compensator until it equals the error in the lens being tested, scale 16 on the casing 18 of the compensator indicating the error. It is to be understood that in the use of my improved lens testing instrument, I do not attempt to determine the power of the lens to be tested directly, the essentialv point being that of employing a standard lens of known power which should neutralize the lens to be tested, my instrument being employed merely to measure the error, if any, in the lens being tested and, consequently, the

same scale will denote the error in the lens irrespective ofthe actual power or form thereof. The errorf can also be measured by a suitable scale upon the image screen by which we could measure the separation between the double images, the error being proportional to the separation. Lenses having different powers 1n different meridians, such as combined sphere and cylinder, can

' also be tested by placing a neutralizing lens shown Yin Fig. XII, maybe actuated to cora lens to be tested, Ya diaphragm adjacent the lthe sphere.

of opposite powers, the axis of the c linder preferably, in the horizontal meri ian in the holder 13, the lens being held in contact with this. The lens will be rotated by hand until the image appears rev lar. If the axis be oblique, the image wi l appear as in Fig. X.` When the axis is placed correctly, any doubling of the horizontal line alone indicates error in the cylinder, and any doubling of the vertical line 'indicates error in Fig. IX illustrates error in both sphere and ycylinder unequalliyl', the error in the cylinder being greater t an in that of the sphere. Displacement of the image,'as shown by the dotted lines in Fig. XI, indicates prismatic effect in the lens being tested, 4which can be read 0E on a suitof plane prisms can yalso be measured this way. When the lens has been correctly positioned, a suitable marking4 device k19, as

reetly mark the lens.

I do not wish to limit myself to'theldetection of the error `inf-the lens heingfteslted by consideration g of the definition Aof, ,fl/the image, but may 'employ my-,instrument' to arranging the holder 13 soA that it might be 4moved a definite amountfatright angles to struction of my instrument should be readily apparent'and it will be seen that I have provided a simple and extremely eflicient instrument vwhich will satisfactorily detect and measure very small errors in lenses, which employs primarily parallel rays for use in testing an unknown lens with a known lens of any standard and which serves to detect the slightest error in the lens being tested and to satisfactorily indicate the amount of such error irrespective of the indicated power of the lens and which on account of the employment of the principle of neutralization in the testing of the lens, will serve to test and measure a lens of any power for which there is astandard for comparison.

Claims:

1. In a lens testing instrument, the com- 'detect movement.` This may be effected. by x bination with means for piojecting an image, of a convergin lens and an image screen 1n the path o the rays, means for -holding a lens to be tested intermediate the projecting means and the screen, means for approximately neutralizing the lens to be tested, and means for accurately determining the residual power of the lens.

2L In a lens testing instrument, the combination with means for projectingv an image, of a converging lens and an image screen in the path of projection, means for lholding a lens to be tested in said path,

age, of' a converging lens and an image screen inthe path of projection, means for holding a lens'to be tested in said path, means for approximately neutralizing the converging lens having aplurality of transparent portions an having a central opaque portion whereby a plurality of images are producedon the image screen when there 1s residual power inthe lens after approximate neutralization thereof, and means for measuring said'residual power.

4. In a lens testing instrument, the combination with means for projecting an image, of a converging lens and screen in the path of projection for forming the image, means for holding a lens to be tested in the path of projection, means for compensating for t e power of the lens, and a diaphragm inserted in the path of projection whereby four separated images are produced on the screen on improper adjustment of the compensating means.

5. In a lens testing instrument, the combination with means for projecting the image of a cross, of a condensing lens, an image screen in the path of projection, means for holding a lens to be tested in the path of projection, means for compensating for the power of the lens to be tested, and a four hole diaphragm disposed in the path of the projection whereby the effect of a double line cross is produced in one or both meridians upon improper adjustment of the compensating means, substantially as described.

In testimon whereof I aiiiX my signature j in presence o two witnesses.

ALFRED H. EMERSON. Witnesses:

FLORENCE E. CODERRE, H. K. PARSONS. 

